Everyone here has made good points, but I haven't seen anyone mention an obvious one.
I am going to buy from crucial at a later time, because I have enough money for the macbook now, without the upgraded ram. I either wait longer to get it upgraded through apple, or I get my macbook now and upgrade to 4gb soon. I'd rather have my macbook now and new ram later, instead of waiting a couple weeks for a macbook with 4gb in it already.
But that is just me.🙂